It’s an annual rite as familiar as April showers; Americans again jumped in their cars in droves this past weekend to celebrate the unofficial start of summer. It was fitting that last week President Obama took a major step, announcing regulations that will increase fuel efficiency within a few years. With this move, Obama ensured that the Memorial Day weekends of the future will not leave as big a carbon footprint.

These standards will save billions of barrels of oil, stop millions of tons of carbon emissions, and may help pull Detroit out of its funk as it forces new rounds of innovation. While the Markey-Waxman bill slowly works its way through the labyrinth in Congress, Obama has taken the single most important step to combat climate change in U.S. history.

This move was bold, but it was also becoming legal necessary. The Supreme Court’s 2007 decision in Massachusetts v. EPA gave that agency precious little wiggle room. It required Obama either to regulate greenhouse gases or deny the science of climate change. No one is surprised that he decided to obey the Court take action.

As a result, Obama is going to start facing many more similar choices. Because the Mass. v. EPA ruling dealt with cars and light trucks, regulating those sources was naturally the first on the list. But this is only the first step. There are petitions on aircrafts, marine vessels, and fuels collecting dust that will need to be wrestled with. The President’s legal obligation to deal with these petitions will likely force additional greenhouse gas regulations into the pipeline in the near future.

In the meantime, Congress is inching closer to passing its own plan to reduce carbon emissions. While there are some legitimate complaints, the Waxman-Markey bill is unquestionably among the most important pieces of environmental legislation ever considered.

But, the Waxman-Markey bill has only passed the first, and one of the easier, hurdles that it will face. The Senate battle is yet to come. To some extent, the bill’s sponsors have reached the top of the foothill, but will now need to climb the mountain. This will be no easy task.

EPA’s legal obligations to continue regulating greenhouse gases can be used as a key point of leverage on the Senate. First came fuel-efficiency standards, soon we may see action on fuels more generally, and eventually the President could even adopt a full cap-and-trade system, complete with auctions and the power to enter into an international agreement.

This dynamic has the potential to keep the pressure Congress: If legislators wait too long, they risk ceding to the EPA their chance to put their stamp on the most important environmental issue of our generation. If environmentalists want to see action in Congress, one of the most important steps they can take is to keep the heat on the President to keep regulations rolling out. As climate change supporters try to carry the bill up over the Senate, having Obama there prodding it along will be sure to help.